Ostariophysi - Evolution

Evolution

Ostariophysian fossils, both anotophysan and otophysian, are known from the early Cretaceous. Ostariophysian fossils are known from every continent except Australia.

Ostariophysians are currently distributed worldwide on all continents except Antarctica. The common ancestor of this group entered fresh water about 251 million years ago coincident with the global decrease in oxygen levels in marine waters. The Otophysi originated in freshwaters during the Jurassic (c. 200-145 Ma) before the breakup of the super continent Pangea. The division of the Otophysi into the four extant clades closely follows the breakup of Pangea. The separation of Laurasia in the north from Gondwanna in the south isolated the lineages which gave rise to the modern Cyprinoformes and Characiphysi. The Characiphysi then was itself divided into the diurnal (day-active) Characiformes and the nocturnal (night-active) Siluriphysi, including Siluriformes and Gymnotiformes. Modern Characiformes are present in both South America and Africa, and have relatively recently extended their range to North America. The Siluriphysi are characterized by many derived traits, including notably, electroreception. The Siluriphysi originated before the breakup of Gondwanna into South America and Africa in the Aptian (c. 110 Ma) but the presence of several basal Siluriphysan taxa in modern South America (Gymnotiformes, Diplomystidae, Loricaridea) suggest that the Siluriphysi may have originated on the western portion of Gondwanna. Alternatively, these basal taxa have subsequently become extinct in Africa. The modern distribution of Siluriformes is cosmopolitan due to subsequest dispersal.

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